Acrylic filaments have always been difficult to dye, and methods for dyeing them have generally included special dyeing techniques and dyes, even when copolymeric dye sites are incorporated in the acrylonitrile polymer of which the filaments are composed. These methods have ordinarily caused the dyeing of acrylic filaments to be carried out in steps separate from the spinning and drawing of the fibers.
The economic and technical advantage of spinning and dyeing as-spun acrylic filaments in a continuous sequence of operations are apparent, and methods for such have been developed for acrylic filaments that are wet-spun. These methods are described in, e.g., Cresswell U.S. Pat. No. 2,558,735, Moore U.S. Pat. No. 3,113,827, Wirth et al. U.S. Pat. No. 3,111,357, Briar et al. U.S. Pat. No. 3,296,341, and Knudsen U.S. Pat. No. 3,242,243. However, because of the inherent differences between wet- and dry-spinning procedures, the techniques that have been developed for dyeing wet-spun acrylic filaments are not well adaptable for use with dry-spun acrylic filaments. Thus, wet-spinning dyeing procedures generally require the formation of a gel of the filament which, of course, is not feasible in a continuous dry-spinning operation. Consequently, methods have been sought to dye dry-spun acrylic filaments continuously during the production of the filaments. This has been termed the "producer dyeing" of filaments.
In preparing such producer-dyed filaments, it had generally been believed that the presence of spinning solvent must be maintained in freshly spun dry-spun acrylic filaments in order to plasticize the fiber and thus aid in taking-up dye. Experience showed that the dye up-take of dry-spun acrylic filaments that had been extracted in hot water at 90.degree.-100.degree.C. to remove the spinning solvent was far too slow to permit continuous spin-dye operations. Moreover, experience showed that dry-spun acrylic filaments extracted at 65.degree.C. to remove solvent did not dye well at a later time when subjected to a dye bath while being stretched.
Accordingly, attempts were made to dye the dry-spun filaments immediately after spinning and before extraction of the solvent. This procedure, however, leads to contamination of equipment used in later steps, as well as to contamination of spinning solvent that is later recovered and recycled, with dye, dye assistants and residual counter-ions originally associated with the dye.
The search for methods of dyeing dry-spun acrylonitrile polymer filaments continuously during the production of the filaments has continued; and it has now been discovered, surprisingly, that substantially undrawn dry-spun acrylic filaments from which the residual spinning solvent has not been removed can be subjected to extraction steps to remove spinning solvent and dyed in an operation continuous with spinning and drawing provided certain process conditions are met. Such conditions include control of temperature during extraction and dyeing (not over 80.degree.C.), control of the amount of liquid remaining on the filaments after extraction and dyeing, and drawing the filaments within certain prescribed limits, provided that substantially no draw is carried out when the filaments first contact the dye.